1. Endocrinology hypothalamo-Pituitary axis
Dr. Hana Alzamil

2. Physiology of hypothalamo-Pituitary axis and regulatory mechanisms
Structure of pituitary gland
Anterior pituitary cell types and hormones
Posterior pituitary cell types and hormones
Hypothalamic control of pituitary gland
Hypothalamo-hypophysial portal system
Hypothalamo-hypophysial tract
Feedback mechanisms
Positive feedback
Negative feedback

3. Structure of pituitary gland
Pituitary gland consist of two lobes
Anterior (Adenohypophysis)
Posterior (Neurohypophysis)

4. Histology of pituitary gland
Anterior pituitary originates from Rathke’s pouch (pharyngeal epithelium)
Posterior pituitary originates from hypothalamus (glial-type cells)
Anterior Pituitary
Posterior Pituitary

5. Structure of pituitary gland (relation to optic chiasm)

6. Hypothalamic control of pituitary secretions
Almost all secretions by the pituitary are controlled by either
Hormonal secretion of hypothalamus
(The anterior pituitary) or
Nervous signals from hypothalamus
(Posterior pituitary)

7. Control of anterior pituitary by hypothalamus
Special neurons in the hypothalamus synthesize and secrete the hypothalamic releasing and inhibitory hormones that control secretion of anterior pituitary
Neurons send their nerve fibers to the median eminence (extension of hypothalamic tissue into the pituitary stalk)
Hormones are secreted to the tissue fluids, absorbed into the hypothalamic-hypophysial portal system and transported to the sinuses of the anterior pituitary

8. Control of anterior pituitary by hypothalamus

9. Structure of pituitary gland
Anterior pituitary contains 5 cell types:
Somatotrops: GH 40%
Corticotrops: ACTH 20%
Thyrotropes: TSH
Gonadotropes: LH & FSH
Lactotrops: PRL

10. Hypothalamic Control of Anterior Pituitary Gland (adenohypophysis)
Anterior pituitary gland is connected to hypothalamus by portal system: “hypothalamic-hypophysial portal vessels”.

11. Hypothalamus and anterior pituitary
Neurosecretory cells secrete releasing factors into capillaries of the pituitary portal system
Factors transported to the anterior pituitary gland to regulate the secretion of pituitary hormones.

12. Hypothalamic releasing and inhibiting hormones
Growth hormone releasing hormone (GHRH)
Stimulates release of growth hormone
Growth hormone inhibiting hormone (GHIH) also called Somatostatin
Inhibits release of growth hormone

13. Hypothalamic releasing and inhibiting hormones
Thyrotropin- releasing hormone (TRH)
Stimulates release of thyroid stimulating hormone (TSH)

14. Hypothalamic releasing and inhibiting hormones
Corticotropin- releasing hormone (CRH)
Stimulates release of adrenocorticotropin hormone (ACTH)

15. Hypothalamic releasing and inhibiting hormones
Gonadotropin releasing hormone (GnRH) –
causes release of the 2 gonadotropic hormones:
Luteinizing (LH)
follicle-stimulating hormone FSH

16. Hypothalamic releasing and inhibiting hormones
Prolactin inhibitory hormone (PIH) also known as Dopamine
Inhibits prolactin secretion

17. Posterior pituitary gland
(Neurohypophysis)

18. Hypothalamic Control of posterior Pituitary Gland (neurohypophysis)
Hormones synthesized in the supraoptic and paraventricular nuclei of the hypothalamus and released in posterior pituitary

19. Secretion of Posterior Pituitary Hormones

20. Hypothalamus and posterior pituitary
Magnocellular neurons in paraventricular and supraoptic nuclei secrete oxytocin and vasopressin directly into capillaries in the posterior lobe

21. Summary of hypothalamic control of pituitary gland

23. Feedback mechanism Positive feedback Negative feedback
Release of hormone A stimulates the release of hormone B
Hormone B stimulates further release of hormone A
Release of hormone A stimulates the release of hormone B
Hormone B inhibits the release of hormone A

24. Negative feedback

25. Positive feedback

26. Negative Feedback mechanism: Long & Short Loop Reflexes

27. Negative Feedback mechanism Cortisol

28. Negative Feedback mechanism Sex steroids

29. Thank you